Hard-disk drives use one or more disks or platters that rotate about a spindle with respect to one or more heads, such as read and/or write heads. The read or write heads read information from or impart information to the disk platters, but do not, in desired operation, physically contact the platters. To the contrary, HDD heads are suspended above the spinning platters by mechanical suspensions. Periodical amplitude modulation on read signals may be caused from the drive head due to a variation in head-disk proximity that may result from mechanical oscillations of the suspension.
Recently, HDD heads have been designed to operate close to platters to communicate therewith. For example, a HDD read head may be positioned very close to a platter to read information from the platter via a reproduction signal. However, close HDD head proximity to the spinning platter increases the risk that the head may come in contact with the platter surface. Contact between a HDD head and a platter may cause performance degradation or destruction of the platter and/or head. An understanding of when a head is likely to contact a platter provides the ability to change operational aspects of the HDD to reduce or eliminate the risk of the head contacting the platter.